1. Field of the Invention
The present invention relates in general to a power-supply distributor for use in vehicles, and more particularly to such a power-supply distributor that distributes power from a battery mounted in vehicles to the various portions.
2. Description of the Prior Art
In the conventional vehicle-mounted power supply, generally, as shown in FIG. 6, power supplied from a battery 1 is first fed to a power-supply block A via a power-supply line 3 protected by a fusible link (FL) 2. Subsequently, power thus fed to the power-supply block A is divided by fuses A1a and A1b to load drive lines 5a and 5b on the downstream side and then fed to loads 6a and 6b via relays A2a and A2b which control load driving, respectively. The load drive lines 5a and 5b employ cables having a diameter which corresponds to the capacity of the load connected thereto. Switches 7a and 7b are used to turn on and off the loads 6a and 6b respectively. When either of those switches is turned on, a relay coil L is conducted to close a relay contact C, electric power is supplied from the battery 1 to the loads 6a and 6b via the fusible link (FL) 2, the fuses A1a and A1l, and the relay contacts C in this order.
One problem to be solved is differences in the specifications of the vehicles. As shown in FIGS. 7(a) and 7(b) respectively, there possibly are, for example, two cases of specifications such that, in one case, the load 6a consists of two bulbs of 60 watts and 12 watts (72 watts in total) and, in the other case, the load consists of two 60-watt bulbs (120 watts in total). In such cases, the abovementioned conventional device needs to change the capacity of the fuse A1a in the power-supply block A correspondingly with the specifications. This would increase the number of parts to be prepared in the power-supply block containing the fuse as the specifications become complicated, reducing productivity and also making it difficult for the manufacturer to manage that number.
Also, in the case where the fuses A1a and A1b are used to protect the load drive lines 5a and 5b and the loads 6a and fib, the fuse capacity is set in standardized step-wise values, for example, 10A, 15A, etc. Thus, the cable may have over-protection from the fuses, as can be seen from the comparison between the current-time characteristics of the fuming of the load drive lines (solid line) and those of the melting of the fuses (broken line) in FIG. 8, thus reducing the efficiency of feeding power. The current-time characteristics of the fuming of the load drive lines are the current over time values causing the burning or smoking of the load drive line cables resulting from the excessive heat generated by the specified amount of current over the specified period of time.
Moreover, as can be seen from the comparison between the motor load constant-current characteristics and lock-current characteristics shown in FIG. 8 and the fuse melting characteristics shown in FIG. 3, the constant-current operation causes no problem, whereas the lock-current operation may cause fuse melting. In order to prevent such problems, the fuse capacity may have to be upgraded by one step.